Add 'benchcomp visualize' & error on regression

[karkhaz]

This commit adds an implementation for the benchcomp visualize
command. Currently, there is one visualization, "error_on_regression",
which causes benchcomp or benchcomp visualize to terminate with a
return code of 1 if there was a regression in any of the metrics.

Users can specify the following in their config file:

visualize:
- type: error_on_regression
  variant_pairs:
  - [variant_1, variant_2]
  - [variant_1, variant_3]
  checks:
  - metric: runtime
    test: "lambda old, new: new / old > 1.1"
  - metric: passed
    test: "lambda old, new: False if not old else not new"

This says to check whether any benchmark regressed when run under
variant_2 compared to variant_1. A benchmark is considered to have
regressed if the value of the 'runtime' metric under variant_2 is 10%
higher than the value under variant_1. Furthermore, the benchmark is
also considered to have regressed if it was previously passing, but is
now failing. These same checks are performed on all benchmarks run under
variant_3 compared to variant_1. If any of those lambda functions
returns True, then benchcomp will terminate with a return code of 1.

This commit fixes #2338.

Testing:

• How is this change tested? Two new regression tests

• Is this a refactor change? No

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[qinheping]

Is it possible to report the name of the regressed benchmark in the error message?
Also, it would be great to have a test that contains metric of more than one benchmark.

[karkhaz]

Done both, thank you! I'm printing it out as a warning to stderr.

Note that this visualization is supposed to be fairly minimal, it's not supposed to be doing fancy output... the idea is that we'd implement more visualizations for Markdown output (for GitHub Actions), HTML reports, etc when we need them. But I do think a warning message to terminal is a good idea here

[qinheping]

Thank you @karkhaz!